Agrilus difficilis

Gory, 1841

honeylocust agrilus, honey locust borer

Agrilus difficilis is a metallic wood-boring beetle in the Buprestidae, commonly known as the honeylocust agrilus or honey . It is associated almost exclusively with honey locust (Gleditsia triacanthos) as its larval . Unlike most Agrilus that develop in dead wood, A. difficilis attacks living trees, particularly stressed or ornamental specimens, and has become a significant pest of landscape honey locusts in the eastern United States. The species is relatively large for the and readily distinguished by its coppery coloration with purple luster and distinctive lateral white pubescent patches.

Pronunciation

How to pronounce Agrilus difficilis: /ˈæɡrɪləs dɪˈfɪsɪlɪs/

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Identification

Distinguished from similar honey locust-associated Agrilus (A. egeniformis, A. fallax, A. pseudofallax) by its relatively large size, coppery color with purple luster, complete absence of spots or pubescent lines on the , and distinctive patches of white along the sides. These develop only in dead wood and are generally smaller with different color patterns.

Appearance

Relatively large for the Agrilus. surface coppery with purple luster. lack spots or pubescent lines. Distinctive patches of white present along lateral portions of and . Underside strongly bronzy green with prominent white densely pubescent patches. Legs more or less coppery.

Habitat

Associated with honey locust trees (Gleditsia triacanthos), particularly in urban and landscape settings where trees may be stressed. Native occur in natural where honey locust grows. are found on foliage and branches of trees.

Distribution

North America. Present throughout the range of its plant Gleditsia triacanthos, which is native to central North America. GBIF records indicate presence in the Nearctic region, with distribution centered in the United States.

Seasonality

begins as early as early June (5 June recorded in 1982) and continues through mid-July (22 July recorded in 1983). Adults are active during spring and early summer, with peak activity likely varying by latitude and local conditions.

Host Associations

Gleditsia triacanthos - larval Almost exclusive ; larvae mine beneath bark of living trees, damaging cambium layer

Life Cycle

Larvae mine beneath the bark of living honey locust trees, feeding on the cambium layer and interfering with movement of water and nutrients. Development occurs in living wood rather than dead branches, distinguishing this from most other Agrilus. emerge through D-shaped exit holes in trunk and main branches.

Behavior

are difficult to detect visually on branches even when present in high numbers; beating branches onto a sheet is required for reliable detection. Under cool, moist, cloudy conditions adults are less active and easier to collect. Adults do not immediately fly when disturbed under such conditions. In sunny, warm conditions adults are highly active and quickly fly from beating sheets.

Ecological Role

A pest that exploits stressed or weakened honey locust trees. In natural settings likely plays a role in of its by attacking declining individuals. In urban landscapes, contributes to tree mortality when trees are planted in suboptimal sites or suffer from stress.

Human Relevance

Significant pest of ornamental honey locust trees in urban landscapes, particularly thornless cultivars widely planted in the eastern United States. cause branch dieback, thinning, and tree death in severe cases. D-shaped exit holes on trunk and branches are diagnostic of infestation. Chemical control is generally not feasible once infestation begins; prevention through proper site selection and tree care is recommended. Economic impact includes tree replacement costs and reduced aesthetic value of landscape plantings.

Similar Taxa

Agrilus egeniformisAlso reared from honey locust, but develops only in dead wood; smaller size and different color pattern
Agrilus fallaxAlso reared from honey locust, but develops only in dead wood; smaller size and different color pattern
Agrilus pseudofallaxAlso reared from honey locust, but develops only in dead wood; smaller size and different color pattern

More Details

Adult Longevity and Fecundity

Based on limited study: females lived significantly longer (48 days) than males (29 days), with average of one per day during a 36-day oviposition period.

Detection Difficulty

are remarkably difficult to spot on branches even when present in large numbers; visual detection of even a few individuals requires close examination of pulled-down branches. This cryptic habit likely contributes to underestimation of sizes and delayed detection of .

Landscape Impact

Honey locust was initially considered relatively free of insect pests when thornless cultivars became popular landscape trees. Agrilus difficilis has proven to be one of several insects that adapted to these plantings, with occasionally causing significant economic damage.